jimmuter

I was reading a 'spy' update from Interbike 2006 here: https://thebicyclechain.com/page.cfm?PageID=254

This frame pump thing sounds interesting. They wrote:

"If Forced Air gets their way you can kiss all your pumps goodbye because their innovative system turns the frame into the pump! And not a wimpy little mini, either, but a powerful compressed-air inflator that'll blast your tires full in 3 seconds and up to 120psi! It's simple, too, just a Schrader valve that manufacturers build into the down tube of their bikes (once Forced Air gets some makers interested). You then fill the down tube with air, and should you flat or need to top off your tires, you simply whip out the hose, which stores in the seatpost, and with an instant pssst, you're ready to roll."

The part I don't get is where they say you then fill the downtube with air. How?

Riv-Lantis

I'm assuming you use your floor pump at home to pump the downtube full of compressed air to use once you have a flat on the road.

It basically just turns the downtube into a compressed air tank.

knobster

Yep, just more weight on the bike.....

CliftonGK1

Unless you fill the d-tube with helium.

sauerwald

I would also be concerned about this putting moisture in the downtube which would encourage corrosion.

Scorer75

I'll say it before someone else does, that's why there's carbon!!!

P.S. I don't own a carbon bike.

cyccommute 

Probably just a bladder in the tube. Would be that hard to do. But would be a bugger to replace if something went wrong with it.

Here's the other issue. I just using wild guess number here but I think I'm close. If you have a down tube that is 3" I.D. and that is 30" long that will give you around 90 cu. in. of air. A 1" tire on a 700C rim has a volume of around 70 cu. in. Not a problem so far because for one tire to get the pressure to 125 psi, you'll need just about the equivalent volume. But, for 2 tires, you are going to need to put double the volume in the same space and the only way to do that is to put in twice the pressure. Now you need 250 psi in 92 cu. in. of the downtube.

Putting 125 psi in a rubber bladder and riding around on it is one thing. If you experience explosive decompression of the tire, it's a loud noise but very little junk get thrown into the air. Putting 250 psi in side a 92cu. in. thin walled metal tube is something else entirely Metal tubes full of high pressure tends to throw sharp little bits of metal in all directions with a pretty good velocity. And those sharp bits don't really care where they go or who they go into.

I just finished an experiment that uses little pipes full of vapor that ran at 145 psi and are a lot smaller than 92 cu. in. Plus those little pipes have 1/4" walls of 316L stainless steel and I take all kinds of precautions like blast screens and containment. I don't think I'd want to be sitting on something with much thinner walls and nearly twice the pressure!

This is one of those goofy ideas that will die an ignomineous death.

FlatFender

I like the idea, but I would be a bit skeptical
I know guys that make bumpers for their 4x4s that hold air but they use really thick walled tubes

2manybikes

DavidLee

... and get rid of my Road Morph? Never!

Da Tinker

If this catches on, then there will be stickers 'This bike is really a pipe bomb.'

radical_edward

Every year, a 'better' mousetrap.

new_dharma

if the tube had air most of hte time, corrosion would not be a problem.

if bikes need to follow traffic laws, would the downtube need a DOT stamp like other compressed gas tanks? would we need a hydro-test every 5 years like SCUBA tanks?

cc_rider

Add an Airzound horn.

Scorer75

You also have to take into account that a tube full of air = finite supply.

That means we still need a pump.

wneumann

Heh. Just build it into the seat. Lord knows my ass bounces up and down enough on some of the rough pavement around here to keep my tires permanently full.

bmclaughlin807

I've seen roll cages built for 4x4's like this... but there's a lot more volume to a roll cage (Or a bumper, as someone else already mentioned)

Bolo Grubb

AGREED!

oboeguy

This appears doomed to failure, IMO, for reasons listed above. CO2 FTW!

dynaryder

Anybody else dig those Sweetskinz tires? Just wish they had them in some narrower designs.

krazygluon

so that would then make 3 things I have to check on my bike for adequate pressure before setting off...

Thanks, but I'll keep my morph.

KnhoJ

Even more! You'd need 150% of that amount, since no air will flow from downtube to tire once the pressures are equal. 375 psi. Then there's the issue of obtaining that pressure in the first place.
And, once you've gone to all that trouble, this kind of pressure has much more interesting applications than inflating tires. Like pneumatic driver education devices! What would an Airzound sound like at 375 psi? Or maybe one of those American Gladiators turrets, with improved ammunition?

procrustes

I don't think a few hundred psi would be very risky in a sealed downtube, if it were it would not be a bike I would want to ride. However I would not want to be straddling anything with a couple thousand psi like what is typically stored in a compressed gas cylinder.

The moisture condensation is a concern - maybe wouldn't be an issue if the schraeder valve were placed at the lowest point. Overall it does sound like an idea not likely to be realistically adopted.

On a related note - I recall reading some article long ago in either a bike or popular science type of magazine. Someone designed a bottom bracket that actually had an internal crank & small piston inside the bottom bracket. The bottom of the downtube was a cylinder in which the piston could compress air or be driven like a motor if the compressed air was released. Thru some series of check valves you could store up compressed air energy (going down hills, etc) and then when going uphill or accelerating you could get some momentary power boost. Sounds a little complicated / impracticle - but kind of an interesting twist on the term "hybrid" bike! Anyone recall that article? - I don't recall if they actually built it or if it was just a thought experiment.

Cheshire

Just build the pumping action into a suspension seat post!! It better have a bleed-off once the chamber is full, though...would hate to be in the middle of a nasty stretch of road and have the seatpost go rigid all of a sudden!

d_D

You have to wonder how these ideas make it so far. Do they not sit down and weight up the advantages/disadvantages against existing products?